Effects of leaf litter water extract of two tree species on the growth and root exudates of ryegrass

To investigate the effects of fallen leaves from Magnolia grandiflora and Taxodium ascendens on the physiological growth and root exudates of perennial ryegrass through potted experiments, different mass concentrations 0 (CK),0.025, 0.1, and 0.2 g·mL⁻¹ of T. ascendens and M. grandiflora were applied to the treatment of perennial ryegrass. The results were as follows: 1) As the concentration of root exudates of two tree species increased, their effects on the root length and seedling height of ryegrass exhibited a “low promotion and high inhibition” pattern. 2) Compared to CK, the activities of superoxide dismutase (SOD) and peroxidase (POD) in ryegrass leaves were significantly increased (P < 0.05), whereas that of catalase (CAT) was notably decreased (P < 0.05). 3) After treatment with leaf litter extracts from two tree species, the chlorophyll content in ryegrass increased and the soluble sugar content decreased. Additionally, there were changes in both the composition and quantity of root exudates. 4) GC-MS analysis showed that there were 83 compounds in root exudates of ryegrass under different treatments, including esters, alkanes, alcohols, and olefins. The results showed that 2,4-ditert-butyl phenol (2,4-D TBP), methyl palmitate (MP), dioctyl phthalate (DOP), and diisobutyl phthalate (DIBP) were different allelopathic substances among different treatment groups. Correlation analysis showed that malondialdehyde (MDA) content was positively correlated with 2,4-D TBP content under treatment with leaf litter extract from M. grandiflora (P < 0.05), whereas the root length was positively correlated with MDA content of ryegrass (P < 0.01). This indicated that the extracts from leaf litter had the potential to modify the secretion of allelochemicals in the root exudates of ryegrass, thereby influencing its growth through the regulation of stress resistance.